FIG. 1 illustrates prior art multimedia system 12. Server 60 provides multiple multicast media streams to multiple end units 20 (which may be set-top boxes, as illustrated in the figure, or other types of end units), via several intermediate systems such as network routers 50 (which may also have Ethernet aggregation switch (EAS) functionalities), digital subscriber line access multiplexers (DSLAM) 40, prior-art customer-premises equipment (CPE) gateways 30. It is noted that while only two routes to multimedia end units 20 that are served by two prior-art CPE gateways 30 which are served by a single network router 50 and/or a single DSLAM 40 are illustrated, it is clear to a person who is skilled in the art that such multimedia systems are adapted to serve much larger numbers of subscribers, and that the diagram is offered for illustration and exemplification purposes only.
Each of the multimedia end units 20 is usually adapted to receive very few concurrent multicasted media streams from the network (a media stream of a TV channel being viewed, for example, as well as potentially other TV channel being recorded for later viewing). Each of those multicasted media streams is transmitted to multiple subscribers according to IP multicast groups that are usually managed by the server 60 (it is noted that multimedia content may be provided to the server from one or more multimedia content providers 70).
In order to switch from one multicasted media stream to another, an internet group management protocol (IGMP) compliant command is issued by the multimedia end unit 20, informing the server that this multimedia end unit 20 wishes to leave a first IP multicast group (associated with the currently transmitted multicasted media stream)—which is known as a “leave” IGMP compliant command, and another IGMP compliant command is issued by the multimedia end unit 20, informing the server that this multimedia end unit 20 want to join a second IP multicast group (associated with the desired multicasted media stream)—which is known as a “join” command. The switching between the two media streams according to these prior art system requires considerable amount of time.